This invention relates to improvements in the manufacture of composite containers and the like of the type wherein the containers are made by an injection blow molding process wherein a preformed liner is placed upon the core, before injection of an outer plastic layer to form a composite parison which is subsequently expanded by internal pressure into the desired form in the manner customary in injection blow molding, the liner and the injected portion of the parison being held at a temperature appropriate for the desired deformation.
More specifically, the invention relates to the production of a novel and improved composite article, consisting of at least two layers of plastic having different properties. Thus, the inner layer may exhibit high resistance to permeation by gases, or solvents, while the outer layer exhibits high mechanical strength at low cost.
It has been heretofore attempted to produce said composite articles by uniting the two layers, such as by heat sealing or solvent bonding. It was found to be difficult to accomplish this purpose, because the two or more layers of plastic usually exhibited different heat expansion and contraction characteristics, which at times resulted in the separation of the several layers whenever the composite article was exposed to changes of temperature, either in the course of manufacture or in subsequent use. The product exhibiting such expansion would be inferior because the two or more layers thereof could not rely on each other for mutual support when exposed to external loads.
At other times, it was found in connection with plastics having well matched expansion properties, that have been caused to weld together, such as by interposition of an adhesive, that the fully, i.e., chemically joined composite assumed the mechanical properties of that layer which was the weakest, a property well known to be typical of composite products made up of layers of different materials. For example, a rupture in either layer tended to be transferred to the adjacent layer.
It is an object of this invention to provide a novel method for the manufacture of a composite article made of several layers of different plastics in which ambient atmospheric pressure is fully utilized to cause the layers to adhere one to the other, to assist the bonding of said layers, such as by welding or by the use of adhesives or to replace such bonding.
It is another object to provide a novel method for the manufacture of composite articles in which several layers, while held together over substantially their entire contacting areas by internal pressure, are nevertheless independent of each other and therefore capable of withstanding their respective ultimate loads.